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Chemistry AS > F322 - Energy > Flashcards

F322 - Energy Flashcards

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0
Q

What is the enthalpy change sign for an exothermic reaction?

A

Negative

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1
Q

What is meant by the term exothermic reaction?

A

A reaction in which heat energy is transferred to the surroundings.

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2
Q

What is meant by the term endothermic reaction?

A

A reaction in which heat energy is absorbed from the surroundings.

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3
Q

What is the enthalpy change sign for an endothermic reaction?

A

Positive

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4
Q

What is activation energy?

A

The energy barrier which must be overcome before a reaction can occur.

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5
Q

What is an example of an exothermic process?

A

Combustion or respiration

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6
Q

What is an example of an endothermic process?

A

Thermal decomposition

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7
Q

What are the standard conditions?

A

Pressure: 100kPa
Temperature: 298K

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8
Q

What is the enthalpy change of reaction?

A

The enthalpy change when amounts of reactants, as shown in the reaction equation, react together to give products in their standard states.

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9
Q

What is the enthalpy change of formation?

A

The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.

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10
Q

What is the enthalpy change of combustion?

A

The enthalpy change when one mole of a fuel reacts completely with oxygen.

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11
Q

Which type of enthalpy process is bond breaking?

A

Endothermic

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12
Q

Which type of enthalpy process is bond making?

A

Exothermic

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13
Q

What is the average bond enthalpy?

A

The amount of energy needed to break one mole of a particular bond in one mole of gaseous molecules.

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14
Q

What is Hess’s law?

A

The total enthalpy change for a chemical reaction is independent of the route by which the reaction takes place, provides the initial and final conditions are the same.

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15
Q

What are the factors that affect the rate of a reaction?

A
  • concentration
  • temperature
  • surface area
  • catalysts
16
Q

How does having a higher concentration increase the rate of a reaction?

A

More frequent collisions between reactant molecules.

17
Q

How does having a higher temperature increase the rate of a reaction?

A

Molecules have more kinetic energy therefore more successful collisions between reactant molecules.

18
Q

How does using a catalyst increase the rate of a reaction?

A

Activation energy is lowered therefore more molecules have the energy to overcome it leading to more successful collisions.

19
Q

What is a catalyst?

A

Chemical which speeds up a her action without being consumed in the overall reaction.

20
Q

Why are catalysts used?

A

Lower temperatures, reduce energy demands so therefore reduces carbon dioxide emissions from burning fossil fuels, allow for better atom economy processes to be used and can increase specificity (enzymes).

21
Q

What does a Boltzmann distribution represent?

A

Number of molecules in a sample with a particular energy.

22
Q

What are the key features of a Boltzmann distribution?

A
  • no molecules have no energy
  • majority of molecules have some energy
  • few molecules have very low or very high energies
  • area under the curve is the number of molecules with that particular energy
23
Q

When does a dynamic equilibrium occur?

A

When the rate of the forward reaction is equal to the rate of the reverse reaction in a closed system.

24
Q

What is Le Chatelier’s principle?

A

The equilibrium will shift so as to minimise the effect of a change applied to a closed system (e.g. concentration, pressure or temperature).

25
Q

What does a catalyst do to a dynamic equilibrium?

A

Accelerates the rate at which the reaction achieves equilibrium as it will increase the rate of the forward and reverse reactions by the same amount.

26
Q

How does changing the concentration affect the position of equilibrium?

A

Increase concentration: shifts away from where the increase occurs

Decrease concentration: shifts towards where the decrease occurs

27
Q

How does changing the pressure affect the position of equilibrium?

A

Increase pressure: shifts to side with fewer moles (of gas)

Decrease pressure: shifts to side with more moles (of gas)

28
Q

How does changing the temperature affect the position of equilibrium?

A

Increase temperature: shifts in direction of endothermic reaction

Decrease temperature: shifts in direction of exothermic reaction

Chemistry AS (7 decks)

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